Methods for fabricating lightweight metal ladders



Nov. 8, 1966 c. E. LARSON METHODS FOR FABRICATING LIGHTWEIGHT METALLADDERS Filed Aug. 23, 1963 2 Sheets-Sheet 1 INVENTOR CLAYTON E. LARSONBY I M JM ATTORNEY i C. E. LARSON Nov. 8, 1966 METHODS FOR FABRICATINGLIGHTWEIGHT METAL LADDERS Filed Aug. 25, 1963 2 Sheets-Sheet 2 IE-T 5.

S 8 M H r W O N A/ S R I .,|||1.l g m I m L E A United States Patent3,283,402 METHODS FOR FABRICATING LIGHTWEIGHT METAL LADDERS Clayton E.Larson, Weston, Conn., assignor to White Metal Rolling & StampingCorporation, Brooklyn, N.Y.,

a corporation of New York Filed Aug. 23, 1963, Ser. No. 304,196 3Claims. (Cl. 29-512) This invention relates to a method for fabricatinga lightweight metal ladder and particularly to a new and improved methodfor fabricating and joining metallic tubular rungs for such ladders tometal side rails.

A predominant trend in recent years in the construction of ladders hasbeen the utilization of lightweight metal such as magnesium and aluminumas the construction material. Lightweight metal provides obviousbenefits since the resulting ladders are easier to carry, maneuver andstore due to their light weight. Also, the low cost and ease offabrication of these metals allow the ladders to be made at a relativelylow cost.

As a result of the advances achieved by the use and the popularity oflightweight metal ladders, there is continuing demand for even lessexpensive and more durable ladders of this type. Ladders, in general,are subjected to rather severe repetitive strains in use and, forreasons of safety and durability, must be extremely resistant to fatigueand/ or loosening of the components under cyclical loading. The laddersmust also be rigid and capable of supporting the heavy loads normallyimposed upon them.

It is, therefore, an object of this invention to provide new andimproved method of fabricating lightweight metal ladders which arerigid, durable and resist loosening of connected parts under therepetitive loadings normal in a ladder structure. Further objectsinclude:

(1) The provision of a new, simple and inexpensive method of fabricatinglightweight metal ladders.

(2) The provision of a new and improved method of joining the rungs of aladder to the side rails in a manner which, while being simple andinexpensive, is light and durable and serves to improve the rigidity ofthe side rails and the total ladder structure.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter; it should be understood, however, that the detatileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

These and other objects will be better understood by those skilled inthe art by reference to the following detailed description and theaccompanying drawings wherein like numbers indicate like parts andwherein:

FIG. 1 is a perspective view (partly broken away) of a ladder embodyingthe features of this invention;

FIG. 2 is an enlarged sectional view of a portion of the ladder of FIG.1 taken along the line 2-2;

FIG. 3 is a still further enlarged and exploded sectional view of aportion of the rung and the side rail of a ladder prior to shaping forassembly;

FIG. 4 is a view similar to FIG. 3 after the components of the ladderhave been shaped for assembly;

FIG. 5 is a View similar to FIG. 4 after assembly and joining of thecomponents of the ladder;

FIG. 6 is a sectional view of the structure of FIG. 5 taken along theline 66 thereof; and

FIG. 7 is a sectional view of the rung of FIG. 5 taken along the line7-7 thereof.

This ladder, in essence, provides a new and improved ladder rung and amethod for forming the rung and ladder side rails for assembly andconnection thereof. Ladders] fabricated by the method of this inventionhave an im-' proved joint between the members. This provides in-'creased rigidity in their side rails, rungs and the ladder structure asa whole is more rigid in torsion and compression. This is achieved byextruding tubular ladder rungs through a corrugated die to producecorrugations on both surfaces of the rung. This provides rigidityincreasing serrations on both the inner and outer surface of the tubularrung, results in a maximum stiffness of the rung with a minimum amountof metal. The ends of the rung are necked down to provide tapered plugthereon while the side rails are perforated with a die in such a manneras to provide a cupped flange around the perforation with the flangehaving rung-matching serrations scored on its inner surface. The flangeis also formed in such a manner to have an inner diameter equal to theaverage diameter of the plug ends. This, on full insertion of the pluginto the flange side of the aperture causes an interference fittherebetween, tightly holding the rung in the aperture and restrainingthe rung from rotation with respect to the side rail. The joint is thencompleted by expanding the plug to conform the end of the plug to thecontour of the flange and aperture, thereby permanently fixing the partstogether.

Referring now to FIGS. 1 and 2 of the drawings, for a more completeunderstanding of the invention, the ladder is composed of rungs 2disposed between side rails 4. The rung and side rail of the ladder arepreferably formed from an extruded lightweight metal, such, for example,as aluminum, magnesium and the like.

Referring to FIG. 3, rung 2 and side rail 4 are shown in their extrudedform prior to shaping thereof for assembly. Side rail 4, in thisembodiment, is in the form of an I beam and comprises web member 6 andcross members 8. Rung 2 in this embodiment, extruded in the form of acylindrical tube, is provided with longitudinally disposed serrations 10and 12 on the external and internal surfaces thereof respectively.Referring to FIG. 7, serrations 10 and 12 are disposed alternativelyaround the periphery of the cross section of the rung to form anessentially corrugated wall therefor. The alternating disposition ofthese serrations produces a corrugated wall configuration which providesa unique advantage in that,

structurally, a maximum stiffness of the rung under lateral loading isachieved with a minimum volume of metal. In other words, a maximumstrength-weight ratio is provided since the corrugations act as aplurality of small, integral stilfeners for the lateral wall.

In an embodiment of the invention utilizing extruded members, theserrations are preferably incorporated in the rung during the extrudingoperation through the use of a serrated or corrugated extruding die. Ifthe rung were formed of rolled sheet metal or the like, the corrugationscould be rolled in the metal sheet in the usual manner prior toformation of the tube member.

Obviously the cross sectional geometry of the rung and related structureis not limited to circular form but could consist of rectangularly ortriangularly configured tubing if so desired.

Returning now to FIG. 3, side rails 4 are cut to suitable length and therequired number of rungs 2 are provided, the rungs being slightlyexcess, in length, of the 'desired spacing between side rail web members6.

FIG. 4 is a view similar to FIG. 3 showing an end of rung 2 and the webmember of the side rail formed and prior to assembly thereof. Rung 2 hasbeen compressed by a suitable tool to form inwardly tapering plug 14 onthe end thereof, the plug also being of reduced darneter to form angularshoulder 16 between the plug portion and the cylindrical portion of therung. Web 6 3 has been punctured by a suitable tool to form aperture 18therethrough. The perforation operation also displaces metal from web 6to provide inwardly extending flange 20 around the periphery of theaperture. Also,

,- during the perforation operation, serrations 22, matching serrations10 on rung 2, are formed on the inner surface of flange 20 by scoring orany suitable means. These serrations may be formed by flutes on one ofthe aperture and flange-forming tools or may be performed separately asdesired. The resulting inner mean diameter is preferably substantiallyequal to the average diameter be tween the mean major and mean minordiameter of plug 14. In preferred form of the ladders, the transverseface of flange 20 is provided with tapered surface 24, substantiallyequal to the angle of shoulder 16. This arrangement creates an extratight connection between the side rails and the rungs.

provides a springing and nesting action against the interior of theflange. After insertion of plug 14 into flange 20, the end of the plugprojecting through aperture 18 is flared outwardly until the .plug endconforms to the inner configuration of aperture 18 and flange 20 asshown. The resulting joint provides a tight, strong connection betweenrung 2 and side rail 4, which, due to the spring quality of the nestingaction, is durable and resists permanent deformation and resultingloosening of the joint under repetitive loading. The depth of theresulting joint also provides a connection which resists angulardisplacement between the rung and side rails and thereby increases therigidity of the rungs and the torsional ladder stiffness in a unique andsimple manner.

Referring to FIG. 6, a sectional view through the complete joint showsthe nesting action between serrations 10 and 22 of the components of thestructure. This nesting action provides, in addition to the benefitsenumerated above,rotational resistance between the rung and side railstructure which is not vulnerable to weakening under repeated cyclicalloadings thereof.

Among the advantages afforded by the method of fabcricating the ladderare the relative simplicity of tooling :and speed of assembly affordedthereby as well as the strong, lightweight and durable resultingarticle. Formation of cups in the web portion of side rail 4, aswell asproviding depth for the resulting joint as described above, alsoincreases the web stiffness of the side rail members by increasing thestructural depth thereof. Flange 20 further provides a greater loadbearing surface between rung 2 and web 6 avoiding concentrated loadingof the web itself. The concentrated loading generally results in wearand loosening of the rung-side rail joint under repeated cyclicalloading. The formation steps provided for by this invention also provideadvantages in that, since severe form-ing operation such as the neckingdown of rung 2 and the perforation and flange forming of web 6 may beperformed prior'to aging of the metal, the final Rockwell hardness ofthe material may be higher than heretofore possible. For example, anextruded aluminum rung having a T4 temper, solution heat-treated but notaged, may be subjected to the severe operation of necking down the endsof the rung without failure. After the severe operations are performedon the rung, and prior to assembling the side rail, the material may beheat-treated to a T6 temper. Similarly, the side rail may also bepunctured and 4 flanged prior to the aging process. The final flaringstep of the assembly is not as severe a working of the material as thatimposed by spinning, beading or other similar operations. The flaringmay be performed on the hardened material without fracture or otherfailure of the metal during assembly. As was pointed out for the rungmember illustrated in this embodiment of the invention, the variouscomponents of the ladder may, of course, be fabricated bymethods-otherithan extruding within the scope of the invention. Forexample, the side rail could, if desired, be formed of sheet metal bentinto any desired channel configuration and thereafter formed inaccordance with the steps outlined above What is claimed as new anddesired to be secured by Letters Patent of the United States is: Iclaim: 1. The method of making a lightweight metal ladder comprising thesteps of:

(A) providing a hollow corrugated ladder rung by:

(a) extruding a metal tube through a corrugated annular die; (b) neckingthe ends of said tube to form shoulders between the tubular portion andthe necked portions thereof, and tapering the neck portions out-. wardlyto provide frusto conical plugs of decreas-- ing diameter outward ofsaid shoulders; (B) providing ladder side rails by:

(a) forming thin metal channels having flatweb portions thereto;

(b) puncturing the web of said rails to form aperr' tures atequally-spaced intervals therealong;

(c) simultaneously cupping the periphery of said apertures to formnormally extending flanges substantially equal in inner diameter to theaverage diameter of said plugs;

(d) simultaneously forming rung-serration matching serrations on theinner surface of said flanges; and (C) assembling said ladder by:

' (a) forcing the plugs of said rung into the flanged sides of theapertures, on said side rails until said shoulders bottom-against theends of said flanges to elastically deform said flanges and said plugsand thereby forming tight interference fits therebetween; and

(b) expanding the outer ends of said plugs to conform to the surfaces ofsaid flange and said web portion to fix said rungs and said side railsfirmly together.

2. The method of making a lightweight metal ladder comprising the stepsof:

(A) providing a hollow ladder rung by:

(a) forming a metal tube having axially disposed serrations thereon;

(b) forming the ends of said tube to have reduced and outwardly taperingplugs thereon of decreasing diameter, toward the end of said tube;

(B) providing ladder side rails by:

(a) forming metal channels having flat web p01.-

tions thereon;

(b) forming apertures in the web of said rails at equally spacedintervals therealong; (c) forming the periphery of said apertures todefine normally disposed flanges therearound substantially equal ininternal diameter to the. average diameter of said plugs;

(d) forming rung serration matching serrations on the inner surface ofsaid flanges; and

(C) assembling said ladder by:

(a) inserting the plugs of saidrungs fully into. the flanged sides ofthe apertures in said side rails to form a tight interference fittherebetween; and

(b) deforming the outer, ends of said plugs to conform to the surface ofsaid flange and said aperture to fix said rungs and said side railsfirmly together.

3. In a method of making lightweight metal ladders having tubular rungsand channel metal side rails, the improvement which comprises:

(A) providing a section of metal tube having axially disposed serrationsthereon;

(B) forming the metal tube to have reduced and outwardly tapering plugsthereon of decreasing diameter toward the end of said tube;

(C) providing metal channels having fiat web portions thereon;

(D) forming apertures in the web of said metal channels at equallyspaced intervals therealong;

(E) forming the periphery of said apertures to define normally disposedflanges therearound substantially equal in internal diameter to theaverage diameter of said plugs;

(F) forming serrations on the inner surface of said flanges matching theserrations on said metal tube;

(G) inserting said plug formed in step B into a flanged side of one ofsaid serrated apertures resulting from step F to form a tightinterference fit therebetween; and

(H) deforming the outer end of said inserted plug of stepf G to conformto the surface of said flange and one of said Web portions to fix saidtube to said metal channel.

References Cited by the Examiner UNITED STATES PATENTS 909,024 l/ 1909Reach 182-194 1,737,780 12/ 1929 Wagenhorst. 2,356,901 8/1944 Wackman29512 2,511,077 6/1950 Race. 1 2,550,070 4/1951 La Brecque et al 29-5122,552,630 5/ 1951 Hutchinson 182194 2,951,550 9/1960 Rich 1821943,037,276 6/1962 Woods 29512 3,119,435 1/1964 Greenman 29512 XR CHARLIET. MOON, Primary Examiner.

1. THE METHOD OF MAKING A LIGHWEIGHT METAL LADDER COMPRISING THE STEPSOF: (A) PROVIDING A HOLLOW CORRUGATED LADDER RUNG BY: (A) EXTRUDING AMETAL TUBE THROUGH A CORRUGATED ANNULAR DIE; (B) NECKING THE ENDS OFSAID TUBE TO FORM SHOULDERS BETWEEN THE TUBULAR PORTION AND THE NECKEDPORTIONS THEREOF, AND TAPERING THE NECK PORTIONS OUTWARDLY TO PROVIDEFRUSTO CONICAL PLUGS OF DECREASING DIAMETER OUTWARD OF SAID SHOULDERS;(B) PROVIDING LADDER SIDE RAILS BY: (A) FORMING THIN METAL CHANNELSHAVING FLAT WEB PORTIONS THERETO; (B) PUNCTURING THE WEB OF SAID RAILSTO FORM APERTURES AT EQUALLY SPACED INTERVALS THEREALONG; (C)SIMULTANEOUSLY CUPPING THE PERIPHERY OF SAID APERTURES TO FORM NORMALLYEXTENDING FLANGES SUBSTANTIALLY EQUAL IN INNER DIAMETER TO THE AVERAGEDIAMETER OF SAID PLUGS; (D) SIMULTANEOUSLY FORMING RUNG-SERRATIONMATCHING SERRATIONS ON THE INNER SURFACE OF SAID FLANGES; AND (C)ASSEMBLING SAID LADDER BY: (A) FORCING THE PLUGS OF SAID RUNG INTO THEFLANGED SIDES OF THE APERTURES ON SAID SIDE RAILS UNTIL SAID SHOULDERSBOTTOM AGAINST THE ENDS OF SAID FLANGES TO ELASTICALLY DEFORM SAIDFLANGES AND SAID PLUGS AND THEREBY FORMING TIGHT INTERFERENCE FITSTHEREBETWEEN; AND (B) EXPANDING THE OUTER ENDS OF SAID PLUGS TO CONFORMTO THE SURFACES OF SAID FLANGE AND SAID WEB PORTION TO FIX SAID RUNGSAND SAID SIDE RAILS FIRMLY TOGETHER.